Dual band antennas for wireless voice and data communications are known. For example, common frequency bands for GSM services include GSM900 and GSM1800. GSM900 operates at 880-960 MHz, and GSM1800 operates in the frequency range of 1710-1880 MHZ. Antennas for communications in these bands of frequencies typically include an array of radiating elements connected by a feed network. For efficient transmission and reception of Radio Frequency (RF) signals, the dimensions of radiating elements are typically matched to the wavelength of the intended band of operation. Because the wavelength of the 900 MHz band is longer than the wavelength of the 1800 MHz band, the radiating elements for one band are typically not used for the other band. In this regard, dual band antennas have been developed which include different radiating elements for the two bands.
In these known dual band antennas, the radiating elements of the GSM1800 Band may be interspersed with radiating elements of the GSM900 Band, or nested within the radiating elements of the GSM900 band, or a combination of nesting and interspersing. See, e.g., U.S. Pat. No. 7,283,101, FIG. 12; U.S. Pat. No. 7,405,710, FIG. 1, FIG. 7. Such nesting and interspersing is achievable, in part, because the radiating elements for the GSM1800 Band do not unduly interfere with the radiating elements for the GSM900 Band and vice-versa.
However, this known solution is not acceptable when high and low bands are sufficiently close in frequency so that coupling occurs between the arrays of radiating elements. Also, multiple radiating elements occupy additional area in an antenna, and add to the costs of an antenna.